More Nuclear Chemistry

Abundance

Binding Energy

Fission

Isotopic Signatures

Nuclear Binding Energy Two Ways

Nuclear Rxn Energy from BE

Molar BE and Element Abundance(Group Work Problem 1)

238U - 206Pb Dating

U23892 Pb206

82 He42

0 e--1+ 8 + 6

t1/2 = 4.468 x 109 years

Assume all 206Pb in a sample is due to 238U decay

206Pb/238U mass ratio gives age

238U - 206Pb Dating (Problem 2 in Group Work)

age = n*length of one half life So, we must find n (how many half lives of 238U have passed)

(N/No) = (1/2)n or log10(N/No) = n[log10(1/2)] or ln(N/No)=n[ln(1/2)] We know N = 10.67 mg How can we find No?

Mass 238U originally ? Mass 206Pb originally = 0 mgMass 238U now = 10.67mg Mass 206Pb now = 2.81 mg

U23892 Pb206

82 He42

0 e--1+ 8 + 6

238U - 206Pb Dating (Problem 2 in Group Work)

U23892 Pb206

82 He42

0 e--1+ + 6

How can we find No? Mass 238U that produced 2.81mg of 206Pb = 2.81mg(238/206) = 3.25mg Original mass 238U = 3.25 mg + 10.67 mg = 13.92 mg

log10(10.67/13.92) = n[-0.301]; n = 0.383 half lives

age = n* t1/2 = (0.393)(4.468 x 109 yrs/half life) = 1.71 x 109 years

Mass 238U originally = 13.92mg Mass 206Pb originally = 0 mgMass 238U now = 10.67mg Mass 206Pb now = 2.81 mg

Nuclear Fission (Consider This 3.53/Problem 3 in Group Work)

Time and Temp Since the Big Bang(Group Work Problem 6)

Isotopic Signatures

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Deuterium Occurs Naturally in Water

1H : 2H ratio in H2O varies slightly with location

ratio is an isotopic signature and can be used as a tracer

Mass Spectrometer(See Group Work Problem 4)

Ion abundance

Mass/charge ratio

Molecule ionized by e- beam

Ion abundance

Molecule enters

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Isotopic Signatures in Tracing

H2O plants animals

1H : 2H in H2O affects 1H : 2H in organism’s H-compounds, so you can trace where an organism has come from by looking at the 1H : 2H of its H-compounds.

Problem in Conservation Biology:How to protect monarch butterfly populations?

Correlate natal sites in North America with wintering sites in Mexico.

focus conservation efforts on most important sites

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Experiment

Rear monarchs in lab on milkweeds gown with known

2H concentration water field on milkweeds naturally watered

by rainfall

Use mass spectrometry to analyze wings for 2H:1H ratio

Results

Lab monarch study: isotope signature in wings highly correlates

to isotope signature of water so isotope signature is a good way to trace where the butterflies originated

Field monarch study: isotope signatures vary depending on site…

Field Study Results

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Isotopic signature in wings depends on natal water 2H:1H ratio

different colors = different 2H:1H ratios

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Natal Origins of Monarch Butterflies Found Wintering in Mexico

Isotope signature studies of wings suggest that few butterflies found in Mexico originate in Canada